I am designing a LED dimmer using software-controlled Pulse Width Modulation, and want to know the minimum PWM frequency that I must reach to make that LED dimming method indistinguishable from variable DC current.
To dim to X% power, the led will be fully on for X% of the PWM period, and fully off for the rest, with X from 0 to 100. I am assuming that the observer can compare with nearby LEDs driven by DC current at various power (but not exactly X% power), and can move the eye (in particular look at the LEDs in peripheral vision, which, I'm told, is the most sensitive to flicker). I disregard purposefully moving one's head relative to the LEDs, which (I guess) could be an effective distinguishing method; and use of a rotating slit disc or similar technique.
I read movie projectors use 48 or 72 Hz shutter frequency (twice to thrice the frame rate) to reduce flicker to something tolerable (but quite noticeable in peripheral vision, I guess). I also read that the 50 or 60 Hz AC frequency has been chosen to avoid flicker, suggesting that that 100 or 120 Hz flicker is perceptible (but the limit could be much higher, because thermal inertia of the filament must damp variations). Another reference point is that CRT with 100 Hz scan rate have been designed, presumably with some benefit (but again that is not an indication of the upper limit).
Edit: Found this relevant post, Effects of high frequency lighting on human vision
Edit: My LED is "white", that is really blue with a luminescence converter consisting of an inorganic phosphor material.